1. Field of the Invention
The present invention relates to a recording apparatus which discharges ink droplets from ink discharge ports provided on a recording head, based on recording data, so as to record images on recording media.
2. Description of the Related Art
Inkjet recording apparatuses have recording heads, configured including an array of ink discharge ports and correspondingly arrayed recording elements. The recording elements are energy generating units for discharging ink droplets, such as heaters, piezoelectric devices, and so forth. Recording scanning, wherein the recording head is moved in the main scanning direction while discharging ink droplets in the recording region, and transporting a recording medium in a sub-scanning direction (which is a direction orthogonal to the main scanning direction), are repeated, whereby an image is recorded on the recording medium.
An arrangement wherein ink droplets could be simultaneously discharged from all ink discharge ports of each ink discharge port rows (recording element rows) of a recording head would be difficult from the perspective of increased costs for the power source of the inkjet recording apparatus, due to the power source capacity which would be necessary for such an arrangement. Accordingly, the recording elements are driven in time-division multiplex fashion to circumvent this problem. Time-division driving can be described as follows. In each ink discharge port row, the recording elements are divided into multiple groups, and recording elements in each group are appropriated to different blocks. The recording elements belonging to the same block are driven simultaneously or generally simultaneously, and the recording elements of each block are driven sequentially with time elapsing therebetween, with all recording elements having been driving following making one cycle. This is repeated in the main scanning direction, thereby performing recording of one main scan in the recording region.
Now, with inkjet recording apparatuses, the recording head may be mounted to the inkjet recording apparatus in an inclined manner due to mounting error of the recording head or assembly error of the recording head. In such cases, there may occur deviation of dot formation positions corresponding to this inclination, which is also known as “inclination shift”. This inclination shift will now be described with reference to FIGS. 30 and 31.
FIG. 30 illustrates the placement of dots formed on a recording medium in a situation wherein a recording head is ideally mounted to the inkjet recording apparatus and there is no inclination shift. In FIG. 30, a recording head 11 is mounted in parallel to the sub-scanning direction indicated by the arrow B, and moves over a recording medium 12 from the left toward the right along the main scanning direction indicated by the arrow A, thereby performing recording. The recording medium is conveyed from the bottom toward the top in the drawing along the arrow B, with the top of the drawing being the downstream side of the sub-scanning direction, and the bottom being the upstream side.
Now, we will say that the recording head 11 has 128 ink discharge ports 13, with recording elements (not shown) disposed correspondingly. These recording elements are divided into eight groups (group 0 through group 7), each having sixteen recording elements. The recording elements of each group are appropriated to different blocks, and the groups are driven sequentially with time elapsing between recording elements in the same block. Here, the recording elements are divided into group 0 through group 7, taking sixteen recording elements in order from the downstream side of the sub-scanning direction. Also, blocks 0 through 15 are appropriated in each group, taking the recording elements in each group from the downstream side of the sub-scanning direction. Thus, the recording elements in the groups are driven in a cycle of the driving order of block 0, block 1, block 2, and so on through block 15.
As long as there is no inclination shift, the dots formed by the one cycle of driving of the recording elements in block 0 through block 15 are formed within the same column (a region having a width of one pixel). FIG. 30 illustrates the placement of dots formed on the recording medium 12 in the event that the recording elements are driven in the order of block 0 through block 15, and three columns worth of recording data, the first column through the third column, has been appropriated to the recording elements. Thus, the dots which the recording elements of each group form by being driven for one cycle are placed within the same column, and an image with high recording quality can be obtained.
On the other hand, FIG. 31 illustrates placement of dots in the event that inclination shift has occurred at the time of recording an image with the same configuration as that in FIG. 30. As shown in FIG. 31, the dots formed by the recording elements appropriated to the same blocks are formed shifted between the upstream side and downstream side in the main scanning direction. Further, there are dots which are formed at positions outside of the columns within which they were supposed to be formed. For example, in group 2, the four dots from blocks 0 through 3 are formed at positions outside of the columns within which they were supposed to be formed. Thus, inclination shift results in dots being formed at positions outside of the columns within which they were supposed to be formed, leading to poor image quality.
Accordingly, there has been proposed a technique for correcting inclination shift with a configuration including a way to detect information relating to inclination shift, and changing the discharge timing of the recording head based on the information relating to inclination shift. Japanese Patent Laid-Open No. 2004-09489 describes an inkjet recording apparatus which performs recording by time-division driving, wherein the discharge timing of the recording head is changed by changing the position of recording data read out from the recording buffer in accordance with the inclination shift.
The inclination shift correction method described in Japanese Patent Laid-Open No. 2004-09489 will be described with reference to FIGS. 32 and 33. This inkjet recording apparatus has the same configuration as that shown in FIG. 30, with the recording elements provided on the recording head 11 being divided into the eight groups of group 0 through group 7, each with sixteen recording elements, and the recording elements of each group being assigned block Nos. 0 through 15. The recording elements in the groups are driven in a cycle of the driving order of block 0, block 1, block 2, and so on through block 15. In this case as well, description will be made regarding an example of using all of the ink discharging ports 13 of the recording head 11 to form dots in the region of three columns, which is the first column through the third column, to record an image.
Also, we will say there that the recording head 11 is mounted inclined in the clockwise direction as to the recording medium 12, with inclination shift occurring such that approximately one column worth of shift is occurring in the main scanning direction between the dot positions formed by the ink discharge ports 13 at both ends of the recording head 11.
FIG. 32 is a diagram illustrating the nozzle Nos. appropriated to the recording elements of group 0 through group 7, the driving Nos., recording data, and dot positions. Note that the dot placement in FIG. 32 schematically illustrates the placement of dots formed on the recording medium 12 in the case that there is no inclination shift. Also, the nozzle Nos. are numbers imaginarily assigned to the recording elements, with 0 through 127 being assigned to the recording elements in order from the downstream side in the sub-scanning direction.
With the configuration described in Japanese Patent Laid-Open No. 2004-09489, the position of the recording data read out form the recording buffer is changed for each group, in accordance with the inclination shift. In the event that there is one column worth of inclination shift, as shown in FIG. 32, the recording data appropriated to the recording elements of group 4 through group 7 is read out having been changed in the main scanning direction by one column from the original column.
Specifically, the recording elements of group 0 through group 3 have assigned thereto the recording data such that dots are formed in the region of the first column through the third column. On the other hand, due to the change in reading position of the recording data, the recording elements of group 4 through group 7 have assigned thereto the recording data such that dots are formed in the region of the second column through the fourth column.
FIG. 33 illustrates the placement of dots actually formed on the recording medium by changing the recording data read position as described with reference to FIG. 32. In FIG. 33, the white circles shown at the position of groups 4 through 7 on the recording medium 12 indicate the positions of dots formed by the recording data of the first column being appropriated to the recording elements of the groups 4 through 7 without the above-described correction having been performed. Due to the inclination shift correction according to Japanese Patent Laid-Open No. 2004-09489, the dots of the groups 4 through 7 are formed at a position offset by one column to the right in the main scanning direction from the position indicated by the white circles. Accordingly, the amount of shift in the main scanning direction can be suppressed for dots in the same block in the downstream and upstream sides in the sub-scanning direction, as can be seen from FIG. 33.
However, the correction method according to Japanese Patent Laid-Open No. 2004-09489 changes the recording data read position for all recording elements within the group. Accordingly, there may be dots in a group regarding which the recording data read position has been changed, that fall outside of the column in which they originally should be. For example, examining the first column of group 4, we can see that if no inclination shift correction is performed, the four dots of blocks 12 through 15 are positioned in the first column, and the remaining twelve dots from blocks 0 through 11 are positioned to the left side from the first column. Assigning the recording data of the first column to a timing for recording in the second column for all recording elements within the group in accordance with this inclination shift correction, the four dots of blocks 12 through 15 will be positioned in the second column instead of the first column in which they originally should have been positioned.
Further, depending on the amount of inclination of the recording head, there may be groups where no correction is performed, even though there are dots at positions outside of the columns in which they originally should be, as with groups 1 through 3.
Thus, with the correction method according to Japanese Patent Laid-Open No. 2004-09489, while the effects of image deterioration due to inclination shift can be alleviated, there also may be cases wherein dots are formed at positions outside of the regions in which they originally should be formed. Also, in the event that the amount of inclination of the recording head is small, there have been cases wherein there are groups regarding which no correction is performed, with dots at positions outside of the columns in which they originally should be formed not being corrected. It can thus be understood that the inclination shift correction method according to the related art is limited in the degree to which deterioration in image quality can be suppressed.